diff --git a/setuptools/discovery.py b/setuptools/discovery.py
index 95c3c7f83ed..45f75acafcd 100644
--- a/setuptools/discovery.py
+++ b/setuptools/discovery.py
@@ -44,12 +44,15 @@
 from pathlib import Path
 from typing import TYPE_CHECKING
 from typing import Callable, Dict, Iterator, Iterable, List, Optional, Tuple, Union
+import warnings
 
 import _distutils_hack.override  # noqa: F401
 
 from distutils import log
 from distutils.util import convert_path
 
+import setuptools
+
 _Path = Union[str, os.PathLike]
 _Filter = Callable[[str], bool]
 StrIter = Iterator[str]
@@ -148,6 +151,13 @@ def _find_iter(cls, where: _Path, exclude: _Filter, include: _Filter) -> StrIter
 
                 # Should this package be included?
                 if include(package) and not exclude(package):
+                    top_package = package.split(".")[0]
+                    if top_package in FlatLayoutPackageFinder._EXCLUDE:
+                        warnings.warn(
+                            f"{top_package!r} is a reserved package name. "
+                            "Please add it to find_package(exclude=...)",
+                            setuptools.SetuptoolsDeprecationWarning,
+                        )
                     yield package
 
                 # Keep searching subdirectories, as there may be more packages